Thermal selectivity of intermolecular versus intramolecular reactions on surfaces

On-surface synthesis is a promising strategy for engineering heteroatomic covalent nanoarchitectures with prospects in electronics, optoelectronics and photovoltaics. Here we report the thermal tunability of reaction pathways of a molecular precursor in order to select intramolecular versus intermolecular reactions, yielding monomeric or polymeric phthalocyanine derivatives, respectively. Deposition of tetra-aza-porphyrin species bearing ethyl termini on Au(111) held at room temperature results in a close-packed assembly. Upon annealing from room temperature to 275 °C, the molecular precursors undergo a series of covalent reactions via their ethyl termini, giving rise to phthalocyanine tapes. However, deposition of the tetra-aza-porphyrin derivatives on Au(111) held at 300 °C results in the formation and self-assembly of monomeric phthalocyanines. A systematic scanning tunnelling microscopy study of reaction intermediates, combined with density functional calculations, suggests a [2+2] cycloaddition as responsible for the initial linkage between molecular precursors, whereas the monomeric reaction is rationalized as an electrocyclic ring closure.We thank the financial support of the EU (projects ERC Starting Grant CHEMCOMP no 279313, EC FP7-PEOPLE-2011-COFUND AMAROUT II program, EC FP7-PEOPLE-2013-CIG (no. 631396) and FEDER CTQ2014-56295-R), the Spanish Ministerio de Economía y Competitividad (MINECO) (projects RYC-2012-11133, RYC-2012-11231, CTQ2014-56295-R, CTQ2014-52974-REDC and Severo Ochoa Excellence Accreditation 2014-2018 SEV-2013-0319), the Comunidad de Madrid (project MAD2D), the Generalitat de Catalunya (2014-SGR-797), the ICIQ Foundation and the IMDEA Foundation

Thermal selectivity of intermolecular versus intramolecular reactions on surfaces

On-surface synthesis is a promising strategy for engineering heteroatomic covalent nanoarchitectures with prospects in electronics, optoelectronics and photovoltaics. Here we report the thermal tunability of reaction pathways of a molecular precursor in order to select intramolecular versus intermolecular reactions, yielding monomeric or polymeric phthalocyanine derivatives, respectively. Deposition of tetra-aza-porphyrin species bearing ethyl termini on Au(111) held at room temperature results in a close-packed assembly. Upon annealing from room temperature to 275 °C, the molecular precursors undergo a series of covalent reactions via their ethyl termini, giving rise to phthalocyanine tapes. However, deposition of the tetra-aza-porphyrin derivatives on Au(111) held at 300 °C results in the formation and self-assembly of monomeric phthalocyanines. A systematic scanning tunnelling microscopy study of reaction intermediates, combined with density functional calculations, suggests a [2+2] cycloaddition as responsible for the initial linkage between molecular precursors, whereas the monomeric reaction is rationalized as an electrocyclic ring closure.Funding agencies: EU (ERC) [279313]; EU (EC) [631396]; EU (FEDER) [CTQ2014-56295-R]; Spanish Ministerio de Economia y Competitividad (MINECO) [CTQ2014-56295-R, RYC-2012-11133, RYC-2012-11231, CTQ2014-52974-REDC, SEV-2013-0319]; Comunidad de Madrid (project MAD2D); Generali</p